1. Field of the Invention
The present invention relates to a calibrating jig, a profile measuring device, and a method of offset calculation in the profile measuring device.
2. Description of the Related Art
Conventionally, there is known a profile measuring device (image measuring device) that measures an outline profile, and so on, of an object-to-be-measured (work) from an image obtained by imaging the object-to-be-measured by an imaging means such as a CCD camera. In addition, there is known a profile measuring device of this kind that is provided also with a noncontact type optical probe, such as a laser probe, or the like, in addition to the imaging means, for improvement of measurement accuracy in a vertical direction, that is to say, a Z direction (for example, refer to patent document 1: JP 11-83438 A).
In a case that an offset exists between an image measuring function of such imaging means and a noncontact displacement detecting function of such noncontact type optical probe, this offset must be quantitatively measured. Various jigs are used for calculation of this offset value.
For example, in patent document 1, there is proposed a calibrating jig in which a metal film of a trapezoidal pattern having two nonparallel linear knife edges is formed on a planar substrate. In addition, there is also known a calibrating jig in which a hollow cylindrically-shaped block 82 having a planer upper surface is formed on a substrate 81, as shown in FIG. 13. There is also calibrating jig in which a rectangular metal block 83 having knife edges at four sides is formed on a substrate 81 and a periphery of the block 83 is surrounded by acrylic blocks 84. This enables image measurement and optical probe measurement of the four sides of the metal block, as shown in FIG. 14. However, there is a problem that, since an error in calculating the offset value in these calibrating jigs depends on a flatness and perpendicularity of the blocks, an adjusting process in an assembled state of components becomes necessary so that the jigs are expensive. Furthermore, in a case of the calibrating jig in patent document 1 and FIG. 14, there is a problem that each of the sides of the block must be aligned with measuring coordinates of a measuring instrument, leading to poor operability.
On the other hand, in three-dimensional measuring instruments using a touch probe, a reference sphere of known radius that is precisely measured beforehand is used for offset calculation for calibration of a device. The reference sphere has an advantage that, since it has no directionality, there is no need for any alignment with the measuring coordinates, or the like. However, in a case of an image measuring instrument, it is difficult to use the reference sphere for offset adjustment. This is because, in a case of image measurement, an edge portion of the reference sphere cannot be clearly determined, whichever kind of illumination, for example, incident-light illumination, transmitted illumination, oblique illumination, and so on, is used. As a consequence, a central position of the reference sphere cannot be accurately calculated.
Accordingly, in response to the above-described problem, patent document 2 (JP 2007-78635 A) discloses a calibrating jig having a sphere and a diffusion surface (a surface that diffuses light). This calibrating jig is for obtaining the offset using an edge between the sphere and the diffusion surface. However, in a case of using the calibrating jig in patent document 2, it is necessary to accurately set a value of a diameter of the sphere, and a distance from a center of the sphere to the diffusion surface of the sphere.
In view of this problem, the present invention has an object of providing a calibrating jig, a profile measuring device, and a method of offset calculation in the profile measuring device in which a cost can be kept low and the offset can be calculated with high precision.